Method for producing a semiconductor layer

ABSTRACT

A method for producing a semiconductor layer is disclosed. One embodiment provides for a semiconductor layer on a semiconductor substrate containing oxygen. Crystal defects are produced at least in a near-surface region of the semiconductor substrate. A thermal process is carried out wherein the oxygen is taken up at the crystal defects. The semiconductor layer is deposited epitaxially over the near-surface region of the semiconductor substrate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Utility Patent Application claims priority to German PatentApplication No. DE 10 2008 027 521.2 filed on Jun. 10, 2008, which isincorporated herein by reference.

BACKGROUND

The present invention relates to a semiconductor device including powersemiconductor components and method of making a semiconductor deviceincluding an epitaxial deposition of a semiconductor layer on asemiconductor substrate.

For some semiconductor components it is necessary to providesemiconductor layers having different properties one above another.Power semiconductor components that require e.g., a lightly dopedsemiconductor layer (drift zone), on a highly doped semiconductorsubstrate layer shall be mentioned here as an example of suchsemiconductor components. Typical representatives of such powersemiconductor components are for example diodes, MOSFETs or IGBTs.

When producing semiconductor layers on a semiconductor substrate, thereis a need for the electrical properties of the semiconductor layer to bekept as stable as possible. For these and other reasons, there is a needfor the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of embodiments and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments andtogether with the description serve to explain principles ofembodiments. Other embodiments and many of the intended advantages ofembodiments will be readily appreciated as they become better understoodby reference to the following detailed description. The elements of thedrawings are not necessarily to scale relative to each other. Likereference numerals designate corresponding similar parts.

FIGS. 1 a to e schematically illustrate embodiments of a semiconductordevice and method for producing a semiconductor device includingproducing a semiconductor layer on a semiconductor substrate.

DETAILED DESCRIPTION

In the following Detailed Description, reference is made to theaccompanying drawings, which form a part hereof, and in which is shownby way of illustration specific embodiments in which the invention maybe practiced. In this regard, directional terminology, such as “top,”“bottom,” “front,” “back,” “leading,” “trailing,” etc., is used withreference to the orientation of the FIGURE(s) being described. Becausecomponents of embodiments can be positioned in a number of differentorientations, the directional terminology is used for purposes ofillustration and is in no way limiting. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

It is to be understood that the features of the various exemplaryembodiments described herein may be combined with each other, unlessspecifically noted otherwise.

One embodiment provides a method for producing a semiconductor includingproducing a semiconductor layer on a semiconductor substrate wherein theelectrical properties of the semiconductor layer are kept as stable aspossible. In one embodiment, the semiconductor is a power semiconductor.

One possibility for realizing such a semiconductor layer construction isthe epitaxial deposition of a semiconductor layer on a semiconductorsubstrate. Epitaxy is understood to mean the growth of monocrystallinelayers on a likewise monocrystalline substrate.

One embodiment relates to a method for producing a semiconductorincluding producing a semiconductor layer on an oxygen-containingsemiconductor substrate, wherein crystal defects are produced at leastin a near-surface region of the semiconductor substrate, at whichcrystal defects the oxygen is taken up when a thermal process is carriedout, and the semiconductor layer is epitaxially deposited over thenear-surface region of the semiconductor substrate after the thermalprocess.

As a result of the oxygen atoms being taken up by the crystal defectsproduced, the oxygen is locally fixed. Consequently, the oxygen cannotdiffuse into the semiconductor layer in subsequent further thermalprocesses. Such oxygen atoms diffusing into the semiconductor layercould form thermal donors in the semiconductor layer, which would havethe consequence of the electrical properties of the semiconductor layerbeing influenced. By preventing this diffusion of oxygen atoms into thesemiconductor layer, the formation of such thermal donors is alsoprevented and the electrical properties of the semiconductor layer canbe kept stable.

FIGS. 1 a to e schematically illustrate embodiments of a semiconductordevice and method for producing a semiconductor device includingproducing a semiconductor layer on a semiconductor substrate.

FIG. 1 a schematically illustrates the production of crystal defects ina semiconductor substrate 10. The semiconductor substrate 10 is amonocrystalline silicon wafer, for example, which contains oxygen,indicated as dots 12 in FIG. 1 a. In this case, the oxygen 12 issituated at interstitial sites in the silicon. Such oxygen-containingsilicon semiconductor wafers are generally produced according to theCzochralski (CZ) method, by pulling a silicon single crystal from asilicon melt and slicing the wafers from this pulled single crystal.Such silicon wafers produced according to the Czochralski methodgenerally have an oxygen concentration [Oi] of 3×10¹⁷ to 10¹⁸interstitial oxygen atoms per cm³. The semiconductor substrate can beprovided with a dopant of one conduction type in order to obtain adesired conductivity. By way of example, for readily conductive(low-impedance) semiconductor substrates, the dopant concentration liesin the range of approximately 10¹⁶ cm⁻³ for 1 ohm to approximately 10²⁰cm⁻³ for 1 mohm cm. In the case of high-impedance semiconductorsubstrates with e.g., 100 ohm cm or more, by contrast, only a low dopantconcentration of 10¹⁴ cm⁻³ or less is present.

Crystal defects are produced in the semiconductor substrate 10 forexample by using high-energy particles. Non-doping particles aretypically used as high-energy particles in order not to influence theelectrical properties of the semiconductor substrate. Such non-dopingparticles are, for example, protons, noble gas ions or semiconductorions, in one embodiment helium ions, neon ions, argon ions, siliconions, germanium ions or krypton ions. The particles are accelerated tovery high velocities, for example, by using an ion accelerator and aresubsequently implanted into the semiconductor substrate 10, which isindicated by arrows 11 in FIG. 1 a. When these high-energy particlespenetrate into the semiconductor substrate, for example vacancies areproduced as crystal defects in the crystal lattice. These crystaldefects are represented as crosses and designated by the referencesymbols 13 in FIG. 1 b. The high-energy particles penetrate, forexample, from a first surface 16 of the semiconductor substrate 10 intothe semiconductor substrate 10 in the direction of a second surface 17,lying opposite the first surface 16, as far as a specific depth T. Thispenetration depth T, also called “end-of-range”, is determined accordingto the implantation energy of the particles. The higher this energy ischosen to be, the deeper the particles penetrate into the semiconductorsubstrate 10; in the extreme case, the semiconductor substrate 10 canalso be penetrated through completely. In one embodiment, thepenetration depth T should be at least 1 μm, and in a further embodimenteven at least 5 μm. Consequently, crystal defects 13 are produced atleast in a near-surface region 14 in the semiconductor substrate 10, asillustrated schematically in FIG. 1 b. However, the crystal defects canalso be produced in the entire semiconductor substrate 10 if thehigh-energy particles completely penetrate through the semiconductorsubstrate 10.

For sufficient crystal defect production by using protons, the radiationdose of the implantation is set for example to 1×10¹³ cm⁻² to 1×10¹⁵cm⁻².

After the production of the crystal defects 13 in at least thenear-surface region 14 of the semiconductor substrate 10, a thermalprocess is carried out at the semiconductor substrate 10. During thisthermal process, the interstitial oxygen atoms 12 are taken up at thecrystal defects 13. The concentration of the free interstitial oxygenatoms 12 in the semiconductor substrate 10 is therefore considerablyreduced, which is illustrated schematically in FIG. 1 c by a smallernumber of the dots 13 that are intended to indicate the interstitialoxygen atoms. In this case, the thermal process includes heating thesemiconductor substrate to temperatures between 700° C. and 1100° C. Theduration of the thermal process is chosen to be between 1 hour and 30hours.

In one embodiment, provision is made, for example, for heating thesemiconductor substrate 10 during the thermal process firstly for afirst time duration, which is shorter than 10 hours, to a temperature ofbetween 750° C. and 850° C. and subsequently for a second time duration,which is longer than 10 hours, to a temperature of between 950° C. and1050° C. In one embodiment, 5 hours can be chosen for the first timeduration and 20 hours for the second time duration. One embodimentprovides for exposing the semiconductor substrate 10 to an inertatmosphere, an atmosphere that does not promote oxidation, such as e.g.,a nitrogen atmosphere, during the thermal process for the oxygen atoms12 to be taken up by the crystal defects 13. In one embodiment,provision can be made for additionally adding a chlorine-containingcompound to this inert atmosphere.

As illustrated schematically in FIG. 1 d, after the thermal process, asemiconductor layer 15 is grown over the near-surface region 14 of thesemiconductor substrate 10. The semiconductor layer 15 is produced inmonocrystalline fashion by epitaxial deposition of a semiconductormaterial. All customary semiconductor materials such as e.g., silicon,germanium, gallium arsenide, indium phosphide or silicon carbide can beused as the semiconductor material. The most insignificant problems withregard to lattice mismatches occur if the same semiconductor material asthat of the semiconductor substrate 10 is used. Thus, in general on asilicon semiconductor substrate 10 a silicon semiconductor layer 15 isalso produced over the near-surface region 14.

The temperatures that occur during the growth phase (indicated by thickarrows at the semiconductor layer 15 in FIG. 1 d) bring about adiffusion of still free interstitial oxygen atoms 12 (indicated as thinarrows in the near-surface region 14 in FIG. 1 d). In one embodiment,the diffusion takes place principally from the region of thesemiconductor substrate which has no crystal defects in the direction ofthe crystal defects or the oxygen atoms already taken up thereby (oxygenprecipitates). In one embodiment, these diffusing oxygen atoms arelikewise taken up by the crystal defects 13. The oxygen precipitatestherefore increase in size. An outdiffusion of oxygen atoms 12 from thesemiconductor substrate 10 into the semiconductor layer 15 produced canthereby be prevented or at least greatly suppressed. Consequently, apossible later formation of thermal donors from interstitial oxygenatoms present in the semiconductor layer 15 can also be prevented or atleast greatly reduced. Uncontrolled and undesirable influencing of theelectrical properties of the semiconductor layer 15 produced cantherefore be avoided at least for the most part.

A semiconductor device including a semiconductor layer 15 producedaccording to the method described above on an oxygen-containingsemiconductor substrate 10 is illustrated schematically in across-sectional view in FIG. 1 e. The semiconductor layer 15 wasproduced with defined properties. The semiconductor layer 15 can have anelectrical conductivity e.g., by being lightly doped with a dopant. Sucha semiconductor layer 15 is used for example as a drift zone or basezone for a power semiconductor component. Especially for powersemiconductor components which have to have a counter-compensation ofthe dopants that is as exact as possible (compensation components), itis important to exactly comply with the doping in the semiconductorlayer 15. The method presented is also suitable for complying with thiscondition.

One embodiment provides for the semiconductor layer 15 to be depositedon the first surface 16 of the semiconductor substrate 10. In this case,the semiconductor layer 15 is directly in contact with the near-surfaceregion 14 in which the crystal defects 13 with the oxygen atoms 12 takenup thereby are produced. Consequently, the oxygen atoms 12 bound inthese oxygen precipitates cannot diffuse into the semiconductor layer15.

One embodiment provides for the semiconductor layer 15 to be depositedon the second surface 17. For this purpose, however, it is necessarythat the previously produced crystal defects 13 reach at least as far as3 μm to the second surface 17. This is the longest range of thegettering effect which the oxygen precipitates produced at the crystaldefects can exert on the free interstitial oxygen atoms 12. Therefore,it is also necessary for this variant that the region 14 of thesemiconductor substrate 10 through which the high-energy particlespenetrate ends at most 3 μm before the second surface 17 of thesemiconductor substrate 10. In other words, the “end-of-range” T shouldbe a maximum of 3 μm away from the second surface 17. Only then is itensured that all the free interstitial oxygen atoms 12 can be taken upby crystal defects before or during the production of the semiconductorlayer 15.

One embodiment provides for the semiconductor substrate 10 to be exposedto a further thermal process prior to the irradiation with high-energyparticles. In one embodiment, the semiconductor substrate 10 is heatedto a temperature of greater than 1050° C. and exposed to an inertatmosphere, for example. One exemplary embodiment provides anitrogen-containing atmosphere for this purpose. This thermal process isintended to bring about an outdiffusion of the free interstitial oxygenatoms 12 from the near-surface regions of the semiconductor substrate inorder thus already to free the near-surface regions of the semiconductorsubstrate 10 of free interstitial oxygen atoms 12. One embodimentprovides for the “end-of-range” to end in the middle of thesemiconductor substrate 10 and for the semiconductor substrate to bethinned at the second surface 17 until the second surface is a maximumof 3 μm away from the “end-of-range”. Another embodiment provides forthe implantation energy of the high-energy particles to be chosen insuch a way that the “end-of-range” is automatically already a maximum of3 μm away from the second surface 17. An additional thinning of thesemiconductor substrate is therefore unnecessary.

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat a variety of alternate and/or equivalent implementations may besubstituted for the specific embodiments shown and described withoutdeparting from the scope of the present invention. This application isintended to cover any adaptations or variations of the specificembodiments discussed herein. Therefore, it is intended that thisinvention be limited only by the claims and the equivalents thereof.

What is claimed is:
 1. A method for producing a semiconductor includinga semiconductor layer on a semiconductor substrate containing oxygen,comprising: producing crystal defects by implanting protons at least ina near-surface region of the semiconductor substrate, the semiconductorsubstrate having a concentration of oxygen between 3×10¹⁷ cm⁻³ and1×10¹⁸ cm⁻³; carrying out a first thermal process, wherein oxygen istaken up at the crystal defects to form oxygen precipitates; epitaxiallydepositing the semiconductor layer over the near-surface region of thesemiconductor substrate after the first thermal process; and diffusingoxygen from the semiconductor substrate from a region of thesemiconductor substrate that has no crystal defects in a direction ofthe crystal defects such that the oxygen is taken up at the crystaldefects to form oxygen precipitates.
 2. The method of claim 1, whereinthe semiconductor substrate is a monocrystalline silicon wafer.
 3. Themethod of claim 2, comprising producing the silicon wafer according tothe Czochralski method.
 4. The method of claim 1, wherein the radiationdose of the protons is between 1×10¹³ cm⁻² to 1×10¹⁵ cm⁻².
 5. The methodof claim 1, comprising wherein the duration of the first thermal processis between 1 hour and 30 hours.
 6. The method of claim 1, comprisingheating the semiconductor substrate during the first thermal process fora first time duration, which is shorter than 10 hours, to a temperatureof between 750° C. and 850° C. and subsequently for a second timeduration, which is longer than 10 hours, to a temperature of between950° C. and 1050° C.
 7. The method of claim 6, comprising wherein thefirst time duration is 5 hours and the second time duration is 20 hours.8. The method of claim 6, comprising wherein, prior to the epitaxialdeposition of the semiconductor layer, the semiconductor substrate isexposed to a second thermal process, wherein the semiconductor substrateis heated to a temperature of greater than 1050° C. and is exposed to aninert atmosphere.
 9. The method of claim 8, comprising carrying out thesecond thermal process out prior to producing the crystal defects. 10.The method of claim 8, comprising exposing the semiconductor substrateto an inert atmosphere during the first thermal process.
 11. The methodof claim 10, comprising adding a chlorine-containing compound to theinert atmosphere.
 12. The method of claim 1, wherein the first thermalprocess comprises heating the semiconductor substrate to a temperaturebetween 700° C. and 1100° C.
 13. The method of claim 1, wherein carryingout the first thermal process comprises carrying out the first thermalprocess in an inert atmosphere.
 14. A method for producing asemiconductor including a semiconductor layer on a semiconductorsubstrate containing oxygen, comprising: producing crystal defects atleast in a near-surface region of the semiconductor substrate byimplanting protons into the semiconductor substrate, the semiconductorsubstrate having a concentration of oxygen between 3×10¹⁷ cm⁻³ and1×10¹⁸ cm⁻³; carrying out a first thermal process in an inertatmosphere, wherein oxygen is taken up at the crystal defects to formoxygen precipitates; epitaxially depositing the semiconductor layer overthe near-surface region of the semiconductor substrate after the firstthermal process; and diffusing oxygen from the semiconductor substratefrom a region of the semiconductor substrate that has no crystal defectsin a direction of the crystal defects such that the oxygen is taken upat the crystal defects to form oxygen precipitates, wherein the protonsat least partly penetrate through the semiconductor substrate.
 15. Themethod of claim 14, wherein a penetration depth T of the protons intothe semiconductor substrate is at least 1 μm.
 16. The method of claim15, wherein the penetration depth T is at least 5 μm.
 17. The method ofclaim 14, comprising effecting the penetration from a first surface ofthe semiconductor substrate in the direction of a second surface of thesemiconductor substrate, lying opposite the first surface.
 18. Themethod of claim 17, comprising depositing the semiconductor layer on thefirst surface of the semiconductor substrate.
 19. The method of claim17, comprising ending the penetrated region of the semiconductorsubstrate at most 3 μm before the second surface.
 20. The method ofclaim 19, comprising depositing the semiconductor layer on the secondsurface of the semiconductor substrate.
 21. The method of claim 14,wherein the first thermal process comprises heating the semiconductorsubstrate to a temperature between 700° C. and 1100° C.
 22. A method ofmaking a power semiconductor comprising: providing a semiconductorsubstrate having a concentration of oxygen between 3×10¹⁷ cm⁻³ and1×10¹⁸ cm⁻³; producing crystal defects by implanting protons at least ina near-surface region of the semiconductor substrate having theconcentration of oxygen between 3×10¹⁷ cm⁻³ and 1×10¹⁸ cm⁻³; carryingout a first thermal process in an inert atmosphere, wherein the oxygenis taken up at the crystal defects to form oxygen precipitates;epitaxially depositing a semiconductor layer over the near-surfaceregion of the semiconductor substrate after the first thermal process;diffusing oxygen from the semiconductor substrate from a region of thesemiconductor substrate that has no crystal defects in a direction ofthe crystal defects such that the oxygen is taken up at the crystaldefects to form oxygen precipitates; and producing the powersemiconductor using the semiconductor layer and semiconductor substrate.23. The method of claim 22, wherein the first thermal process comprisesheating the semiconductor substrate to a temperature between 700° C. and1100° C.
 24. A method for producing a semiconductor including asemiconductor layer on a semiconductor substrate containing oxygen,comprising: producing crystal defects in an entirety of thesemiconductor substrate by implanting protons into the semiconductorsubstrate; carrying out a first thermal process in an inert atmosphere,wherein the oxygen is taken up at the crystal defects to form oxygenprecipitates; and epitaxially depositing the semiconductor layerdirectly over the semiconductor substrate after the first thermalprocess.
 25. The method of claim 23, wherein a duration of the firstthermal process is between 1 hour and 30 hours.